Method and device for producing synthesis by partial oxidation of slurries made from fuels containing ash with partial quenching and waste heat recovery

ABSTRACT

A method and a device for the gasification of solid fuels such as bituminous coal and coke such as bituminous coal, lignite, and biomass, as well as petroleum coke, that are finely ground and mixed with water or oil to make fuel-liquid suspensions, so-called slurries, and their gasification together with an oxidizing medium containing free oxygen by partial oxidation at pressures between atmospheric pressure and 100 bar, and at temperatures between 1200 and 1900° C., in an entrained flow reactor. The method includes the steps of slurry preparation and infeed to the reactor, gasification in an entrained flow reactor with cooled reaction chamber contour, partial quenching, waste heat recovery, and wet or dry dust separation, with the crude gas being pretreated so that it can be fed to other technological steps such as crude gas conversion or desulfurization.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a gasification method and a device forimplementing the method. The method consists of the process steps ofslurry preparation, fuel infeed, gasification reaction, partialquenching, gas scrubbing, and partial condensation. Gas scrubbing andpartial condensation can be replaced by mechanical dust separation, toproduce gases containing CO and H₂ by partial oxidation of powderedfuels containing ash with a gasification medium containing free oxygen,at high temperatures and elevated pressure.

To achieve long operating times, the pressurized jacket of thegasification reactor has to be protected reliably against the action ofcrude gas and against the high gasification temperatures of 1200-1900°C. This is done by confining the reaction or gasification chamber with acooled tubular shield that is hung in the pressurized jacket. Theannular gap between tubular shield and pressurized jacket is flushed.

The fuel as a slurry is brought to the gasification pressure by pumptransport and is fed to the head of the reactor through burners. One ormore fuels or varieties of coal can be gasified at the same time. Thecrude gas leaves the gasification chamber together with the liquefiedslag at the bottom of the reactor and is then partially cooled to 700°C. to 1100° C. by injecting water, and is freed of entrained fines afterrecovering the waste heat. The scrubbed crude gas is then fed to furthertreatment steps.

2. The Prior Art

The autothermic entrained flow gasification of solid, liquid, andgaseous fuels has been known in the technology of gas production foryears. The ratio of fuel to gasification medium containing oxygen ischosen so that higher carbon compounds are completely cracked forreasons of synthesis gas quality into synthesis gas components such asCO and H₂, and the inorganic components are discharged as molten slag;see J. Carl, P. Fritz, NOELL-KONVERSIONSVERFAHREN, EF-Verlag für Energieund Umwelttechnik GmbH, 1996, p. 33 and p. 73.

According to various systems used in industry, gasification gas andmolten slags can be discharged together from the reaction chamber of thegasification device, as shown in DE 197 131 A1. Either systems withrefractory linings or cooled systems are used for the inner confinementof the reaction chamber structure of the gasification system; see GermanPatent No. DE 4446 803 A1.

European Patent No. EP 0677 567 B1 and PCT Publication No. WO 96/17904show a method in which the gasification chamber is confined by arefractory lining. This has the drawback that the refractory masonry isloosened by the liquid slag formed during gasification, which leads torapid wear and high repair costs. This wear process increases withincreasing ash content. Thus, such gasification systems have a limitedservice life before replacing the lining. Also, the gasificationtemperature and the ash content of the fuel are limited. Feeding in thefuel as a coal-water slurry causes considerable losses of efficiency—seeC. Higman and M. van der Burgt, “Gasification”, Verlag ELSEVIER, USA,2003—which can be prevented or reduced by using oil as a carrier mediumor by preheating the coal-water slurry. A quenching or cooling system isalso described, with which the hot gasification gas and the liquid slagare carried off together through a conduit that begins at the bottom ofthe reaction chamber, and are fed into a water bath. This jointdischarge of gasification gas and slag can lead to plugging of theconduit and thus to limitation of availability.

German Patent No. DE 3534015 A1 shows a method in which the gasificationmedia, powdered coal and oxidizing medium containing oxygen, areintroduced into the reaction chamber through multiple burners in such away that the flames are mutually deflected. The gasification gas loadedwith powdered dust flows upward and the slag flows downward into aslag-cooling system. As a rule, there is a device above the gasificationchamber for indirect cooling utilizing the waste heat. However, becauseof entrained liquid slag particles, there is the danger of depositionand coating of heat exchanger surfaces, which hinders heat transfer andmay lead to plugging of the pipe system and/or erosion. The danger ofplugging is counteracted by cooling the hot crude gas with a circulatedcooling gas.

Ch. Higman and M. van der Burgt in “Gasification”, page 124, VerlagElsevier 2003, describe a method in which the hot gasification gasleaves the gasifier together with the liquid slag and directly enters awaste heat boiler positioned perpendicularly below it, in which thecrude gas and the slag are cooled with utilization of the waste heat toproduce steam. The slag is collected in a water bath, while the cooledcrude gas leaves the waste heat boiler from the side. A series ofdrawbacks detract from the advantage of waste heat recovery by thissystem, such as the formation of deposits on the heat exchanger tubes,which lead to hindrance of heat transfer and to corrosion and erosion,and thus to lack of availability.

Chinese Patent No. CN 200 4200 200 7.1 describes a “Solid PulverizedFuel Gasifier”, in which the powdered coal is fed in pneumatically andgasification gas and liquefied slag are introduced into a water baththrough a central pipe for further cooling. This central discharge inthe central pipe mentioned is susceptible to plugging that interfereswith the overall operation, and reduces the availability of the entiresystem.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a gasificationmethod that takes into account the different ash contents of fuels andhas high availability, with reliable operation.

This task is accomplished by a gasification method for the gasificationof solid fuels containing ash with an oxidizing medium containingoxygen, in a gasification chamber designed as an entrained flow reactor,at pressures between atmospheric pressure and 100 bar, in which thereaction chamber contour is confined by a cooling system, with thepressure in the cooling system always being chosen to be higher than thepressure in the reaction chamber. The method is distinguished by thefollowing features:

The fuel, e.g. bituminous coal, bituminous coke and lignite coke, aswell as biomass coke and/or petroleum coke and/or their mixtures, arepulverized to a grain size of <500 μm, preferably <200 μm, and are mixedto make a fuel-in-water or fuel-in-oil suspension, a so-called slurry,by adding liquids such as water or oil. Stable solids concentrations ofup to 70 wt. % are achieved when using water as the carrier medium withadded surfactants. These are brought to the desired gasificationpressure of up to a maximum of 100 bar by means of suitable pumps, andare fed for the gasification reaction through suitable burners that areattached at the head of the gasification reactor. The fuel concentrationin the slurry and the amount of flowing slurry are monitored, measured,and regulated by measurement devices, control devices, and monitors. Anoxidizing medium containing free oxygen is fed to the burner at the sametime, and the fuel is converted into crude synthesis gas by partialoxidation. The gasification takes place at temperatures between 1,200°C. and 1,900° C. at pressures up to 100 bar. The reactor is equippedwith a cooling shield that consists of water-cooled pipes weldedgas-tight.

The hot crude synthesis gas leaves the gasification chamber togetherwith the liquid slag formed from the fuel ash, and arrives at a chamberperpendicularly under it, in which partial quenching occurs by injectingwater or by feeding in a cold gas, whereby it is cooled to temperaturesbetween 700° C. and 1,100° C. At this temperature, the entrained liquidslag has been cooled to the extent that it can no longer adhere to themetallic surfaces. The crude gas cooled to temperatures of 700° C. and1,100° C. then arrives at a waste heat boiler together with the likewisecooled solid slag, to utilize the sensible heat for steam production.This partial quenching or partial cooling prevents or sharply reducesthe risk of slag caking on the waste heat cooling pipes. The water orrecycled gas condensate needed for the partial quenching is fed inthrough nozzles that are located directly on the jacket. The cooled slagis collected in a water bath located at the bottom of the waste heatboiler. The crude gas, cooled to 200° C.-300° C., leaves the waste heatboiler at the side and reaches a crude gas scrubber, suitably a Venturiscrubber. The entrained dust is thereby removed down to a grain size ofabout 20 μm. This degree of purity is still inadequate for carrying outsubsequent catalytic processes, for example crude gas conversion. Italso has to be considered that salt mists are also entrained in thecrude gas, which have detached from the powdered fuel duringgasification and are carried off with the crude gas. To remove both thefine dust <20 μm and the salt mists, the scrubbed crude gas is fed to acondensation step in which the crude gas is chilled indirectly to about5° C. to 10° C. Water is thereby condensed from the crude gas saturatedwith water vapor, which absorbs the described fine dust and saltparticles. The condensed water containing the dust and salt particles isseparated in a following separator. The crude gas purified in this waycan then be fed directly, for example, to a crude gas converter ordesulfurization system.

Instead of the scrubbing and condensation steps, a mechanical dustseparator can be provided that operates at 200° C. to 300° C., for whichcentrifugal separators or filter systems can be used.

BRIEF DESCRIPTION OF THE DRAWINGS

Other objects and features of the present invention will become apparentfrom the following detailed description considered in connection withthe accompanying drawings. It is to be understood, however, that thedrawings are designed as an illustration only and not as a definition ofthe limits of the invention.

In the drawings, wherein similar reference characters denote similarelements throughout the several views:

FIG. 1 shows a lock diagram of the technology;

FIG. 2 shows a gasification reactor with partial quenching andperpendicularly arranged waste heat boiler; and

FIG. 3 shows a gasification reactor with partial quenching and adjacentwaste heat boiler.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

320 tons/hour of bituminous coal with a composition of C 71.5 wt. %  H4.2 wt. % O 9.1 wt. % N 0.7 wt. % S 1.5 wt. % Cl 0.03 wt. %, an ash content of 11.5 wt. %, and a moisture content of 7.8 wt. %, is tobe gasified at a pressure of 40 bar. The calorific value of the coal is25,600 kJ/kg. The gasification takes place at 1,450° C. 245,000 m³(standard)/h of oxygen is needed for the gasification. The coal is firstfed to a state-of-the-art grinder in which it is pulverized to a grainsize range between 0 and 200 μm, and is then mixed in a special system 1according to FIG. 1 with water with added surfactants to make a stablecoal dust in water suspension, the so-called slurry. The solidsconcentration in this slurry is 63 wt. %, and the amount of slurry is485 tons/hour. The slurry is brought to the desired gasificationpressure of 100 bar by means of a pump suitable for pumping solid-liquidsuspensions, and is fed to the burner of the gasification reactor 2 ofFIG. 1 through the supply line 1.1, with the amount being monitored,measured, and regulated. To conserve oxygen, the slurry can be preheatedup to 400° C., depending on the gasification pressure, prior to beingfed into the gasification reactor 2.

FIGS. 2 and 3 show the gasification reactor. The slurry flowing to thegasification reactor through the feed line 1.1 at 465 tons/hour issubjected to partial oxidation at 1450° C. along with the 245,000 m³(standard)/hour of oxygen flowing to the gasification chamber 2.3through the line 2.1, with 565,000 m³ (standard)/hour of crude gas beingformed with the following composition: H₂ 18.5 vol. % CO 70.5 vol. % CO₂ 6.1 vol. % N₂  2.3 vol. % NH₃ 0.003 vol. %  HCN 0.002 vol. %  H₂S  0.5vol. % COS  0.07 vol. %.

The gasification chamber 2.3 is confined by a cooling shield 2.4 thatconsists of a water-cooled tube system welded gas-tight. The crude gastogether with the liquid slag flows through the outlet opening 2.5 intothe chamber 3.1 for partial quenching/partial cooling of the crude gasto temperatures of 700° C.-1,100° C. At this temperature, along with thecrude gas, the slag is also cooled to such an extent that it cannot bedeposited in the pipes 4.1 of the waste heat boiler that followsaccording to FIG. 1. The steam generated in the waste heat boiler 4 isutilized in the process to preheat the oxidizing medium containingoxygen or as a gasification moderator to preheat the slurry. The slag iscollected in a water bath 4.2 located at the bottom of the waste heatboiler and is discharged through 4.3. The crude gas leaves the wasteheat boiler through 4.4 and arrives at crude gas scrubber 5 according toFIG. 1. Waste heat boiler 4, however, can be located according to FIG. 3directly beneath gasification reactor 2 and partial quencher 3, butalso, as shown in FIG. 4, beside it. In this case, there is a slagdischarge 4.3 beneath partial quencher 3 and also one below waste heatboiler 4.6. The crude gas leaving waste heat boiler 4 through outlet 4.4then arrives at the crude gas scrubber 5 according to FIG. 1, which isan adjustable Venturi scrubber to which is fed about 100 m³/h of washwater. The wash water is freed of absorbed solids in the usual way andis fed again to the Venturi scrubber. The wash water can be preheated inorder to wet the crude gas further at the same time as the washing. Toremove fine dust <20 μm in size and salt mists not separated in theVenturi scrubber, the water-washed crude gas is subjected to partialcondensation 6 according to FIG. 1, with the crude gas being chilledindirectly to about 5-10° C. The finest dust and salt particles aretaken up by the water vapor condensing during the chilling and thusremoved from the crude gas. The crude gas cleansed of solids then hasthe following composition: H₂ 13.4 vol. % CO 51.4 vol. % CO₂  4.5 vol. %N₂  1.5 vol. % NH₃ 0.0022 vol. %  HCN 0.0012 vol. %  H₂S 0.36 vol. % COS0.05 vol. % H₂O 37.30 vol. % 

The purified, wet crude gas amounts to 775,000 m³ (standard)/hour. Itcan be directly sent to a crude gas converter or to other treatmentsteps.

Accordingly, while only a few embodiments of the present invention havebeen shown and described, it is obvious that many changes andmodifications may be made thereunto without departing from the spiritand scope of the invention.

LIST OF REFERENCE NUMERALS

-   1 Slurry preparation and infeed-   1.1 Slurry line-   2 Reactor-   2.1 Line for oxygen-   2.2 Burner-   2.3 Gasification chamber-   2.4 Cooling shield-   2.5 Outlet opening-   3 Quenching cooler-   3.1 Quenching chamber-   3.2 Nozzles in 3-   3.4 Transfer line from 3 to 4-   4 Waste heat boiler-   4.1 Cooling pipes in the waste heat boiler 4-   4.2 Water bath with slag in 4-   4.3 Slag discharge from 4-   4.4 Opening from 4 to the crude gas scrubber 5-   4.5 Water bath with slag 4-   4.6 Slag discharge from 4-   5 Crude gas scrubber-   6 Partial condenser

1. A method for the gasification of fuels such as bituminous coals andcokes such as bituminous, lignite, biomass, and petroleum coke in theentrained flow with an oxidizing medium containing free oxygen, themethod comprising the following steps: slurrying a pulverized fuel witha grain size <200 μm with water with added surfactant, to obtain afuel-in-water slurry with a solids concentration of 40-70 wt. %;bringing the slurried fuel to a gasification pressure of 100 bar bypumping, for which the slurry is preheated to temperatures up to 400°C.; feeding the fuel to the reactor through a supply pipe together withan oxidizing medium containing free oxygen; subjecting the fuel topartial oxidation in the reaction chamber at pressures betweenatmospheric pressure and 100 bar, the reaction chamber having a contourconfined by a cooling shield; melting ash of the fuel; transferring themelted ash through a discharge device to a quenching chamber of aquenching cooler along with hot crude gas; partially quenching the crudegas in the quenching cooler with cooling of the crude gas totemperatures between 700 and 1,100° C.; cooling the partially quenchedcrude gas in a waste heat boiler to temperatures between 150 and 400° C.with generation of steam; subjecting the cooled crude gas to a crude gasscrubber and partial condensation, or to dry mechanical dust separationby centrifugal force or filtration, to separate entrained dust; andsending the cooled gas freed of dust to additional treatment steps.
 2. Amethod pursuant to claim 1, wherein a crude gas scrubber is used, andthe crude gas scrubber is a single- or multiple-stage Venturi scrubber.3. A method pursuant to claim 2, wherein the Venturi scrubber issupplied with fresh water or recycled condensates that result from thecooling of the gas.
 4. A method pursuant to claim 1, wherein the wasteheat boiler is operated at temperatures of 700 to 1,100° C.
 5. A methodpursuant to claim 2, wherein the crude gas scrubbing takes place attemperatures of 150 to 300° C.
 6. A method pursuant to claim 2, whereinthe Venturi scrubber is supplied with circulated water or recycledcondensate.
 7. A method pursuant to claim 1, wherein the fuel issupplied to the reactor as a fuel-in-water slurry.
 8. A method pursuantto claim 1, wherein the fuel is supplied to the gasification reactorthrough one or more burners.
 9. A method pursuant to claim 1, whereingranulated slag from the quenching cooler is discharged through one ormore outlets from the quenching cooler.
 10. A method pursuant to claim1, wherein the partially quenched gas leaves the quenching coolerthrough one or more gas outlets.
 11. A method pursuant to claim 1,wherein one or more varieties of coal are gasified at the same time. 12.A method pursuant to claim 1, wherein the amount of slurry in the supplypipe is measured, monitored, and regulated.
 13. Device for gasificationof fuels such as bituminous coals and cokes such as bituminous, lignite,biomass, and petroleum coke in the entrained flow with an oxidizingmedium containing free oxygen, comprising: a system for producing andfeeding slurry; a reactor for the gasification of supplied powdered fuelwith an oxidizing medium containing free oxygen, comprising a supplypipe for the slurried fuel and a line for the oxidizing medium, burnersfor feeding the slurried fuel and oxidizing medium into a reactionchamber of the reactor, said reaction chamber having a cooling shieldconsisting of water-cooled pipes welded gas-tight, and an outlet device;a quenching cooler with no internals connected to the reactor via theoutlet device, the quenching cooler having nozzles arranged in one ormore nozzle rings through which is sprayed water for partial quenching,said nozzles being integrally incorporated in an inner jacket; a wasteheat boiler following the quenching cooler; and equipment for purifyingthe gasified fuel.
 14. A device pursuant to claim 13, wherein a reactionchamber of the quenching cooler is connected directly to the waste heatboiler, in which heat of the crude gas is utilized through tubes toproduce steam, and wherein there are discharge openings in a bottom ofthe waste heat boiler for crude gas and for slag withdrawal with a waterbath.
 15. A device pursuant to claim 13, further comprising a crude gasscrubber and a partial condensation system following the crude gasscrubber for purification.
 16. A device pursuant to claim 15, whereinthe crude gas scrubber is a single- or multiple-stage Venturi scrubber.17. A device pursuant to claim 13, further comprising a mechanical drydust separator for gas purification.
 18. A device pursuant to claim 15,wherein there are further gas treatment stages connected in line afterthe water scrubber and partial condenser or the mechanical dry dustseparator.
 19. A device for gasification of fuels such as bituminouscoals and cokes such as bituminous, lignite, biomass, and petroleum cokein the entrained flow with an oxidizing medium containing free oxygen,comprising: a system for producing and feeding slurry; a reactor forgasification of supplied fuel dust with an oxidizing medium containingfree oxygen, the reactor comprising a supply pipe for receiving slurriedfuel and a line for the oxidizing medium, said slurried fuel andoxidizing medium being fed by burners into a reaction chamber of thereactor, said reaction chamber comprising a cooling shield made ofwater-cooled pipes welded gas-tight and a discharge device; a quenchingcooler connected to the discharge device; a waste heat boiler connectedto the quenching cooler via a transfer line for receiving partiallycooled crude gas, said boiler being equipped with boiler tubes andutilizing heat of the crude gas to produce steam; a crude gas scrubberand a partial condensation system following the crude gas scrubber, or amechanical filtration dust separator.
 20. A device pursuant to claim 19,further comprising water baths in both the quenching cooler and thewaste heat boiler, in which water baths cooled slag is collected.
 21. Adevice pursuant to claim 19, further comprising devices for dischargingslag on both the quenching cooler and the waste heat boiler.